Integrated: 8302108: Clean up placeholder supername code

[Coleen Phillimore]

On Thu, 9 Feb 2023 15:46:47 GMT, Coleen Phillimore <coleenp at openjdk.org> wrote:

> Please review change to make PlaceholderEntry::_supername a SymbolHandle to correctly refcount the symbol rather than have ad-hoc code.  It also moves the private functions to private and asserts invariant that find_and_remove must always find a matching entry.  Finally, this also more eagerly removes the supername symbol from the placeholder entry, so I have to fix the test in https://github.com/openjdk/jdk/pull/12491 before pushing this.
> Tested with tier1-4.

This pull request has now been integrated.

Changeset: abbeb7e4
Author:    Coleen Phillimore <coleenp at openjdk.org>
URL:       https://git.openjdk.org/jdk/commit/abbeb7e4d2f5739dff77b2c79e675fb69368db1e
Stats:     53 lines in 4 files changed: 13 ins; 24 del; 16 mod

8302108: Clean up placeholder supername code

Reviewed-by: dholmes, iklam

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PR: https://git.openjdk.org/jdk/pull/12495